<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ::placeholder{
            color:aqua;
            font-size: 12px;
            font-weight: 700;
            font-style: italic;
        }
        /* google浏览器 & 苹果浏览器 */
        ::-webkit-input-placeholder{
            color:aqua;
            font-size: 12px;
            font-weight: 700;
            font-style: italic;
        }
        /* div里面的字体默认是16,但是input里面的字体默认是12px */
    </style>
</head>
<body>
    <input type="text" placeholder="请输入姓名">
    <div>请输入姓名</div>
</body>
</html>